1. Field of the Invention
The present invention relates generally to a method for making organic electroluminescent displays, and more particularly to a method for making cathode ramparts and insulating layer of an organic electroluminescent display through only one photo mask.
2. Description of the Related Art
With the advent of the information technology age, there is an increasing demand for high-quality electro-optical displays, in which liquid crystal displays (LCD) are the most popular. A LCD backlight module comprising a light guide and a reflective plate is utilized for introducing the light beams, emitted from the cold cathode fluorescent lamp, vertically to the liquid crystal display panel, in which the liquid crystal contained therein controls the illuminance of the LCD. Conventional LCDs have a limited view angle and require very complicated manufacturing processes, which result in high manufacturing costs and relatively low yields. However, organic electroluminescent displays (OELD) have larger view angles and can be produced through less complex manufacturing process. These advantages are based on the self-luminance of the organic elements in the organic electroluminescent displays, which results in the unrestricted view visual, more natural colors displayed, increased operational temperature range and shorter response time.
With reference to FIG. 1, the structure of a conventional organic electroluminescent display 1 is shown. A glass substrate 2 carries a plurality of first display electrodes 3 arranged in parallel and a plurality of cathode ramparts 4 made of an electrical insulation material are formed on the substrate 2. The cathode ramparts 4 are arranged perpendicular to the first display electrodes 3 and apart from each other, and are protruded from the substrate and exposes at least portions of the first display electrodes 3. Each cathode rampart 4 at the upper part thereof has an overhang portion 7 protruded in a direction parallel to the substrate 2. Between the cathode ramparts 4, organic electroluminescent layers 5 are formed on the exposed first display electrodes 3, and a plurality of second display electrodes 6 are formed on the organic electroluminescent layers 5.
With reference to FIG. 2A-2F, a conventional manufacturing process of an organic electroluminescent display is shown. A plurality of first display electrodes 210 of stripe shapes arranged in parallel are formed on a glass substrate 200 by a sputtering process, as shown in FIG. 2A. A layer of insulating material 220 is spin-coated on the substrate 200 with the first display electrodes 210 disposed thereon. Then, shadow masks are disposed on the insulating material 220, and after a photolithography process, openings 225 having a direction perpendicular to that of the first display electrodes 210 are formed, thereby exposing the first display electrodes 210 partially, as shown in the top view of FIG. 2B and the sectional view of FIG. 2C. Next, as shown in FIG. 2D, a layer of photoresistant material 230 is formed on the insulating material 220 having openings 225. With reference to FIG. 2E, photo masks 235 are formed on the photoresistant material 230 and are illuminated by parallel light beams I. Due to the mask effect of the photo masks 235, only the portions of the photoresistant material 230, i.e. the mesh areas, are illuminated by the light beams I. Subsequently, a developing process is conducted on the photoresistant material 230 so as to form a shape of cathode ramparts shown in FIG. 2F. Finally, an organic electroluminescent material is formed on the exposed first display electrodes and then a plurality of second display electrodes are formed on the organic electroluminescent material such that an organic electroluminescent display is completed.
In the prior manufacturing processes of an organic electroluminescent display, two photo masks are required for the formation of the cathode ramparts; the first photo mask is utilized for forming openings in the insulating materials, and the second photo mask is utilized for forming cathode ramparts.